1. Field of the Invention
This invention relates to a pin tractor for feeding blank paper for use in various printers, typewriters, etc. which are used as output devices for electronic computers, especially for personal computers.
2. Description of the Prior Art
In various printers, typewriters, etc. which are used as output devices for electronic computers, etc., pin tractors are generally used which feed blank paper by engaging pins of an endless belt carrying pins with feed perforations at both edges of blank paper and by running the endless belt carrying pins. Such pin tractors, are disclosed by U.S. Pat. No. 4,130,230 and Japanese Utility Model Registration Application Laying Open Publication No. 60-191450, for example, are so designed that an endless belt carrying pins engages with and is driven by a toothed pulley which is run by a driving shaft and is rotatably supported between two members forming a frame.
Since pin tractors feed blank paper at a fixed speed by engaging pins of a belt with feed perforations at each edge of the blank paper, it is necessary that the right and left belts carrying pins which engage with each edge of the blank paper turn synchronously. Therefore, if the pin tractor is of such construction that a toothed driving pulley is arranged between two members forming a frame, it is difficult to properly synchronize pins of the right and left belts carrying pins, when fitting a pin tractor to a driving shaft.
In the conventional pin tractors mentioned above, for the purpose of reducing the turning torque of a toothed driving pulley for driving the belt carrying pins is mounted rather loosely and is caused to run straight in an open guide groove made in a frame. More particularly, the guide groove has guide surfaces close to both edges of the belt carrying pins, which runs with its blank paper feeding surface (surface of the belt base) almost on the same level with the surface of the frame. Therefore, when the blank paper is being fed, a blank paper feeding load is generated due to sliding resistance between the blank paper and the surface of the frame, with a reduction in the blank paper feeding efficiency, especially in the case where blank paper quality is rough. Also, if the belt carrying pins is loose, when blank paper is fed on the belt loosening side the belt lifts considerably and blank paper feeding accuracy is reduced.
In the above pin tractor, as described in the specification of U.S. Pat. No. 4,214,691, for example, a frame is supported movably in relation to a guide shaft and a driving shaft which are arranged in parallel with each other and the position of the frame is adjusted according to the width of blank paper to be fed. A locking means is also provided for fixing the frame to the guide shaft at the desired position.
The above locking means comprises a tubular fixing member put on the guide shaft of the frame and a lever member rotatable on said fixing member. Also, the frame is formed of two members so that it can support a toothed pulley from both sides. Therefore, more parts are required, manufacturing cost is higher and assembly is more troublesome.